The present invention relates to light emitting element driving circuits, communications devices, and light emitting element driving methods. In particular, the present invention relates to light emitting element driving circuits and light emitting element driving methods for driving surface-emitting elements, and communications devices equipped with the circuits.
The laser driving circuit described above changes the bias current based on the amount of emission light of the VCSEL, thereby driving the VCSEL in a manner that the amount of emission light therefrom becomes generally constant. The amount of emission light of the VCSEL decreases when the temperature rises. Therefore, when the amount of emission light decreases, the laser driving circuit increases the bias current to be supplied to the VCSEL, thereby keeping the amount of emission light at constant. Also, the laser driving circuit described above increases the modulation current to be superimposed on the bias current with an increase in the temperature.
[Non-patent Document 1] “+3.0 to +5.0, 2.5 Gbps VCSEL and Laser Driver”, [online], Maxim Integrated Products, [Searched on May 11, 2004], Internet <URL: http://pdfserv.maxim-ic.com/en/ds/MAX3996.pdf>
A communications device such as an optical transmission device that uses a VCSEL as a light source may be disposed in a place where the ambient temperature rises to a high temperature such as a device interior of a router or the like. In this case, because the conventional laser driving circuit described above increases the bias current and the modulation current with an elevation in the temperature of the VCSEL, a substantially large amount of current is supplied to the VCSEL. Accordingly, the conventional laser driving circuit described above has a problem in that the power consumption of the device having the VCSEL provided therein increases. Also, because an extremely large amount of current is supplied to the VCSEL, there are problems in that the VCSEL is rapidly deteriorated, and its service life is shortened.
Accordingly, it is an aspect of the present invention to provide light emitting element driving circuits, communications devices and light emitting element driving methods, which can solve the problems described above. This aspect can be achieved by combinations of the characteristics recited in independent claims in the Scope of Patent claims. Also, their dependent claims specify further advantageous concrete examples of the present invention.